Synaptic organization in the mammalian cochlear nucleus, the first central auditory system nucleus, will be analyzed in this proposed light (LM) and electron (EM) microscopic study. Four basic questions about direct and indirect connections between cochlear fibers and identified "octopus neurons" in the cochlear nucleus will be emphasized. First, a previous hypothesis that single cochlear axons can produce cytologically different (heterotypic) synapses upon octopus cells will be evaluated. Second, morphological differences among central cochlear fibers or their branches in the octopus cell area (OCA), indicating different inputs to octopus cells, will be studied. Third, any direct input from specific cochlear regions directly to individual octopus cells will be analyzed to determine any cochleotopic distribution to the OCA. Fourth, intrinsic connections between octopus cells and other neurons of the cochlear nucleus will be studied for patterns ana cytology of their synpatic connections. If the other neurons receive direct cochlear inputs and also project to octopus cells, then they would provide indirect cochlear input to the OCA. This fourth part of the project will necessitate continued morphological study of the dorsal cochlear nucleus (DCN) that lies superficial to the OCA. The proposed description of OCA synaptic organization can be compared with OCA response patterns to normal auditory stimuli in order to explain central processing of peripheral auditory information. Confirmation of heterotypic synapses would reveal an unusual structural organization used by the CNS.